A variety of different sole constructions are used by the footwear industry. For the most part, each sole construction has characteristics that make it particularly well-suited for specific applications. For example, some sole constructions are selected for their durability, others for their flexibility and comfort, while still others are selected for their aesthetic appeal.
One well-known construction method, known as a welt construction, typically includes a strip of material such as leather or hard rubber that is used to secure the shoe sole and the shoe upper together. Welt construction typically involves a number of manufacturing steps. First, the upper is wrapped around a last and secured to the insole by stitching, stapling or other securing mechanism. Once the upper is lasted, a welt is usually secured to the upper and insole by stitching. The midsole may also be secured to the bottom of the upper/insole assembly by stitching that extends through the base portion of the welt and the midsole. Although this type of shoe construction provides a certain degree of durability and aesthetic appeal, it usually requires numerous manufacturing steps and thus increased costs of production. The other problems associated with this type of shoe construction are heaviness and decreased flexibility of the shoe.
It is also known to cement components of a shoe together, such as an upper to an outsole. Typically, this process involves numerous manufacturing steps. First, the surfaces to be cemented, or glued, need to be cleaned and readied, which may also include roughening. Further, there may be an application step where the cement is applied to the surfaces, which further involves measuring and evenly distributing the glue over the surface. Further, there may be a pressing step where the surfaces are pressed together in order to reduce air that may be trapped between the surfaces and enhances adhesion. Once the components are pressed together, cementing often requires a waiting period for the cement to dry. Thus, one of the problems with the cementing process is the number of steps and time involved, which in turn negatively affects cost and efficiency. Additionally, the cementing process may be further complicated if the surfaces to be glued are uneven or difficult to reach.
Another known type of shoe construction is an Opanka construction, wherein the outsole of the shoe is typically sewed to the upper of the shoe along an outer periphery of the outsole. An example of Opanka construction is described in U.S. Pat. No. 7,322,128 to Issler. FIG. 1 shows a shoe 10 having an upper 11 that is secured to the outsole 12 by a stitch 13 in the fore part of the shoe 10. The stitch passes through the upper 11 into a first channel 14 on the outsole 12, and then into a second channel 15 on the outsole 12. It is apparent that this type of construction or stitching produces two rows of visible stitching: an upper row is formed in the first channel 14 and a lower row is formed in the second channel 15. In the rear part of the shoe 10, as shown in FIG. 2, a different type of the stitch 18 is used, which passes the thread through the outsole 12, the upper 11, and a liner 19. The shoe 10 further includes a sockliner 20 sewn to the liner 19 within the shoe upper 11.
However, there are several problems associated with this type of construction. First, having an outsole that shows two rows of stitching may detract from the appearance of the shoe. Second, the lower row of stitching is more likely to be damaged by walking, and such damage could cause the shoe to fall apart. The two rows of stitching make the shoe less durable.
Similar problems are also present in other known types of shoe constructions. For example, U.S. Pat. No. 4,505,055 to Bergmans discloses a shoe structure wherein the outsole has a sidewall that extends around its circumference. The lip has a vertical outer face and a ledge that projects horizontally. The upper rests on the ledge, and stitching extends through the upper and the lip. However, the stitching also extends through an insole and is exposed on the interior of the shoe. Such a design leads to discomfort to the wearer, since the wearer's foot will rub against the stitching.
U.S. Application Serial No. 2005/0172514 to Wu discloses a shoe construction in which the outsole includes a barrier wall that extends around the periphery of the shoe. The upper is attached to the outsole by stitching that extends through the outer periphery of the upper into a channel formed by the barrier wall and out of the side surface of the outsole. Thus, the construction requires two rows of stitching that are visible on the outside of the shoe, which decreases the aesthetic appeal and the durability of the shoe.
What is needed, therefore, is an improved shoe construction technique by which a shoe may be constructed in a more efficient manner, and by which manufacturing costs are reduced and that involves fewer manufacturing operations. Another desire is to provide a shoe wherein the stitching used for securing the outsole to the upper is only minimally visible on the outside of the shoe to enhance aesthetics. Yet a further desire is to provide a shoe that is comfortable to wear and that protects a wearer's foot from uncomfortable contact with stitching.